With the development of IT infrastructure, it became possible to accumulate a large amount of multimedia data (documents, videos, images, sounds, various log data, and the like) in a large capacity storage. In order to extract information efficiently from a large amount of accumulated data, various information extraction/search techniques for individual media data have been developed and put to practical use.
As an example of information extraction of multimedia data, a technique of detecting an object (indicating an object that is desired to be extracted or a part thereof, for example) or a specific region included in an image is considered. The detecting of an object in an image or the specifying of a region in an image corresponds to morphological analysis (a means of dividing a document into words and determining a part of speech) in document analysis, and it is an important technique in analyzing the meaning of an image.
As a technique of detecting an object in an image, a technique disclosed in Non-Patent Document 1 is widely known and input into production as a face recognition function in a digital camera or a monitoring system. In the technique disclosed in Non-Patent Document 1, a large amount of sample images of an object serving as a detection target are collected, and a plurality of weak identifiers are generated based on luminance values of the images through machine learning. An object region is specified by searching for partial regions in the image fully using a robust identifier obtained by coupling the weak identifiers.
At the present time, a frontal face of a person is commonest as a category of an object serving as a detection target. However, when a wide range of content accumulated in a storage is set as a target, it is desirable to set various categories such as vehicles, animals, buildings, diagrams, and various goods as a detection target. Further, in order to process a large amount of data, it is necessary to improve analysis process efficiency.
With respect to the improvement in the analysis process efficiency, Patent Document 1 described below discloses a technique of limiting a region that undergoes image processing for detecting an object region using an existence probability of an object. The technique disclosed in Patent Document 1 decides a region that undergoes image processing using static information of an imaging system such as a focal distance or a resolution, and is considered to be effective in an environment in which a photographing environment or a photographing device is limited as in an in-vehicle camera, and structured data is managed.